//whileÇ¶Ì×if²âÊÔ£¬Çó¸ø¶¨ÊýÒÔÄÚËùÓÐÅ¼ÊýµÄºÍ
int a = 1 ;

int main(){

    int i = 1,sum=0,N ;
    scanf(N);

    while(i < N){
       if(i%2 == 0){
           sum = sum +i;
       }
       i = i + 1;
    }
    printf(sum);
}

